In order to connect to a network, a wireless device (e.g., a user equipment (UE)) needs to acquire network synchronization and obtain essential system information, including system information in the Master Information Block (MIB) and Remaining Minimum System Information (RMSI). Synchronization signals are used for adjusting the frequency of the device relative to the network. Synchronization signals are also used for finding the proper timing of the received signal from the network. In New Radio (NR), the synchronization and access procedure may involve several signals, including the Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), Physical Broadcast Channel (PBCH), and Synchronization Signal and PBCH Block (SSB or SS/PBCH block).
The PSS allows for network detection in the presence of a high initial frequency error (up to tens of ppm). The SSS allows for more accurate frequency adjustments and channel estimation while at the same time providing fundamental network information (e.g., cell ID).
The PBCH provides a subset of the minimum system information for random access and configurations for fetching the remaining minimum system information in RMSI. The PBCH also provides timing information within a cell (e.g., to separate timing between beams transmitted from a cell). The amount of information that can be fit into the PBCH is highly limited to keep the size down. Furthermore, demodulation reference signals (DMRS) are interleaved with PBCH resources to allow it to be received properly.
The SSB includes the above signals (i.e., PSS, SSS and PBCH DMRS) and PBCH. The SSB may have different subcarrier spacing (SCS) (e.g., 15 kilohertz (kHz), 30 kHz, 120 kHz or 240 kHz) depending on the frequency range.
In NR, RMSI is carried in PDSCH scheduled by the Physical Downlink Control Channel (PDCCH) in the Control Resource Set (CORESET) configured by PBCH. The RMSI contains the remaining subset of minimum system information (e.g., the bit map of the SSBs that are actually transmitted).
A number of SSBs (typically rather close in time) constitute an SS burst set. An SS burst set is transmitted periodically. The periodicity is configured in RMSI. For initial access, a 20 millisecond (ms) SS burst set periodicity is assumed. FIGS. 1 and 2 below illustrate the SSB mapping within slots and SS burst set mapping to slots within 5 ms, respectively.
FIG. 1 illustrates an example of SSB symbols in slots. More particularly, FIG. 1 illustrates the SSB mapping for different SCS (including 15 kHz, 30 kHz (Pattern 1), 30 kHz (Pattern 2), 120 kHz, and 240 kHz). For the 15 kHz, 30 kHz (Pattern 1), 30 kHz (Pattern 2), and 120 kHz SCS, the SSB mapping within two slots (Slot n and Slot n+1) is shown. As illustrated in FIG. 1, each slot contains 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols (depicted as boxes numbered 0-13). For the 240 kHz SCS, the SSB mapping within 4 slots (Slot n, Slot n+1, Slot n+2, and Slot n+3) is shown. For the 240 kHz SCS example, each slot contains 14 OFDM symbols (depicted as boxes numbered 0-13).
In the example of FIG. 1, the OFDM symbols in brackets are mapped to a candidate SSB position. Each candidate SSB position includes 4 OFDM symbols. For instance, for the example of 15 kHz SCS, Slot n includes two candidate SSB positions: a first that includes OFDM symbols 2-5; and a second that includes OFDM symbols 8-11. Slot n+1 also includes two candidate SSB positions: a first that includes OFDM symbols 2-5; and a second that includes OFDM symbols 8-11. The mapping for the 30 kHz (Pattern 2) SCS is the same as that for the 15 kHz SCS.
For the example of 30 kHz (Pattern 1) SCS, Slot n includes two candidate SSB positions: a first that includes OFDM symbols 4-7; and a second that includes OFDM symbols 8-11. Slot n+1 also includes two candidate SSB positions: a first that includes OFDM symbols 2-5; and a second that includes OFDM symbols 6-9. The mapping for the 120 kHz SCS is the same as that for the 30 kHz (Pattern 1) SCS.
For the example of the 240 kHz SCS, some of the candidate SSB positions extend across the slots. For example, Slot n includes a first candidate SSB position including OFDM symbols 8-11. A second candidate SSB position extends across Slot n and Slot n+1, including OFDM symbols 12-13 of Slot n and OFDM symbols 0-1 of Slot n+1. Slot n+1 further includes a third candidate SSB position including OFDM symbols 2-5 and a fourth candidate SSB position including OFDM symbols 6-9. Similarly, Slot n+2 includes a first candidate SSB position that includes OFDM symbols 4-7 and a second candidate SSB position that includes OFDM symbols 8-11. A third candidate SSB position extends across Slot n+2 and Slot n+3, including OFDM symbols 12-13 of Slot n+2 and OFDM symbols 0-1 of Slot n+3. Slot n+3 further includes a fourth candidate SSB position that includes OFDM symbols 2-5 and a fifth candidate SSB position that includes OFDM symbols 6-9.
FIG. 2 illustrates an example of SS burst sets in slots within 5 ms. More particularly, FIG. 2 illustrates an example of SS burst sets in a half radio frame of 5 ms. In the example of FIG. 2, each box is a slot. As shown in FIG. 2, an SS burst set is mapped to slots within a 5 ms window in a compact manner with a mapping pattern, resulting in high network energy efficiency. The position of possible SSB locations in a slot is illustrated in FIG. 1 and, as described above, the position of possible SSB locations depends on the SCS. The mapping patterns of SSB have a periodicity of 2 slots (for SSB with SCS value 15 kHz, 30 kHz or 120 kHz) and 4 slots (for SSB with SCS value 240 kHz). And with this periodicity of 2 or 4 slots, SSB mapping can be continued via repeating the pattern until the maximum number of SSBs are fully mapped.
Before Radio Resource Control (RRC) connection, there are access messages and system information that need to be transmitted to a wireless device on PDSCH. These messages and information can be, for example, RMSI, other system information (OSI), paging, Random Access Response (RAR) (message 2) and message 4, etc. Existing approaches to time domain resource allocation for messages and system information that need to be transmitted on PDSCH before RRC connection suffer from certain deficiencies. For example, existing approaches may lack flexibility in terms of the time domain resource allocation table that can be used. Thus, there is a need for a time resource indication mechanism for transmitting and receiving PDSCH carrying information and/or messages before RRC connection.